Vibration of the speaker membrane, without signal, causes back EMF producing current that flows in opposite direction working against membrane motion, hence damping vibration. This current (damping effect) depends on the total resistance in the circuit including amp’s output, wires resistance, woofer’s choke resistance and speaker’s impedance (source impedance) itself, that is mostly resistive. All this will limit maximum possible "DF" to about 1. As long a amplifier doesn’t add to this limitation, there should be no difference in sound. AMP with DF =10 will affect overall damping only by 10%. Very high DF (my amp has 4000), come either from the output configuration or negative feedback used to reduce distortions, widen the bandwidth etc. Even shallow 20dB negative feedback will reduce output impedance ten times.
Damping Factor plays one very important role - it can be used to impress customers.
As for NGF - it is a wonderful tool when it is used wisely. It improves pretty much everything (bandwidth, distortions, output impedance etc). It might produce TIM distortions (higher odd harmonics, overshoot in time domain) for faster changing signals, because of increased amps gain caused by late summing of delayed output signal (phase shift). Reducing bandwidth at the input, perhaps to one that amp had without feedback, should prevent TIM. That would require designing a stable wide bandwidth amp with low distortions to start with. The main problem is that designers use cheap parts and poor circuits trying to fix it with deep feedback. For instance, very popular output transitors 2N3055 have very nonlinear h21e (Beta) - a current gain vs current. There are much better choices but they cost more money (2N3055 cost less than $1). NGF is pretty much free.
Damping Factor plays one very important role - it can be used to impress customers.
As for NGF - it is a wonderful tool when it is used wisely. It improves pretty much everything (bandwidth, distortions, output impedance etc). It might produce TIM distortions (higher odd harmonics, overshoot in time domain) for faster changing signals, because of increased amps gain caused by late summing of delayed output signal (phase shift). Reducing bandwidth at the input, perhaps to one that amp had without feedback, should prevent TIM. That would require designing a stable wide bandwidth amp with low distortions to start with. The main problem is that designers use cheap parts and poor circuits trying to fix it with deep feedback. For instance, very popular output transitors 2N3055 have very nonlinear h21e (Beta) - a current gain vs current. There are much better choices but they cost more money (2N3055 cost less than $1). NGF is pretty much free.
